The present invention relates generally to containers for heating or cooling materials such as food, beverages, medicines, and the like and, more specifically, to a container that includes an internal module that adds heat to or removes heat from the materials in the surrounding container.
Containers may have integral modules for warming materials in the container, such as Japanese sake, coffee, or soup. Examples of such self-heating containers are disclosed in U.S. Pat. No. 4,640,264, issued to Yamaguchi et al. , and U.S. Pat. No. 4,784,113, issued to Nagai et al. Such containers typically include an outer can, in which the food or beverage is sealed, and a sealed module or inner can that contains two chemical reactants. The reactants are stable when separated from one another but, when mixed, produce an exothermic reaction. It is known that combinations of other reactants will produce endothermic reactions to cool the container contents. (Both types of reactions involve a change in enthalpy.)
The inner can is typically disposed adjacent one end of the outer can. The inner can has two chambers, each of which contains one of the chemical reactants, separated by a breakable barrier such as metal foil or a thin plastic film. Typically, one of the reactants is in solution and the other is in a solid powdered or granular form. A rod extends into the outer can at the end adjacent the inner can. One end of the rod is adjacent to the barrier, and the other end terminates in a button outside the outer can. To initiate the reaction that warms or cools the contents of the outer can, the can is disposed with that end upright. Depressing the button forces the rod downward, breaking the barrier and allowing the liquid reactant to drop into the solid reactant. The end of the rod may have a flared head to facilitate complete puncturing of the barrier. The heat produced by the resulting exothermic reaction or used by the resulting endothermic reaction is transferred between the inner can and the contents of the outer can by conduction. Exothermic reactions also typically generate a gas, which is allowed to escape through vents in the end of the container. When the reaction has stopped, the container is inverted. The second end of the outer can has a seal, such as pull-tab, that may be opened and through which the user may consume the heated contents.
Self-heating and self-cooling containers known in the art are uneconomical to manufacture because the mechanism for puncturing the foil barrier commonly has multiple components. The inner can contains the solid reactant and has a short, tubular cap sealing one end. The cap contains the liquid reactant. One end of the cap is sealed with the foil barrier, and the rod extends through an opening in the other end of the cap. Depressing the button forces the rod to slide in the opening until it punctures the foil barrier. Practitioners in the art have found that forcing a rod through the foil opens a large passage through which the liquid reactant can flow, thereby minimizing the time required for the liquid to drain from the cap into the remainder of the inner can. However, fabricating and assembling the multiple components increases the cost of the container. Furthermore, liquid can leak between the rod and the opening in the cap through which the rod moves. Practitioners in the art have therefore disposed a ring of wax around the rod where it exits the inner can to improve sealing. The step of adding the wax, however, increases the manufacturing complexity and, ultimately, cost of the container. Self-heating and self-cooling containers known in the art may also leak the powdery material that is the product of the completed reaction through the vents when the container is inverted. It would be desirable to provide an inner can or module that has both a minimal number of separate parts and maximal resistance to leakage. It would also be desirable to provide such a container with improved sealing between the inner can or module and the outer can. These problems and deficiencies are clearly felt in the art and are solved by the present invention in the manner described below.